Abstract

Azufre Volcano (21°47?S, 68°15?W), located in the Altiplano-Puna Volcanic Complex of the Andean Central Volcanic Zone (CVZ), is formed by two coalescent edifices (Northern and Southern) constructed between 120 and 1300 kaExtensive hydrothermal alteration occurred within a host sequence of andesites/dacites (120–700 ka in age) in the Northern edifice. The silica content of the erupted lavas of this volcano range from ?60% m/m (andesite) to ?67% m/m (dacite). These lavas have 87Sr/87Sr ratios ranging from 0.7066 to 0.7074, 143Nd/144Nd ratios ranging from 0.51229 to 0.51239, and quartz ?18O values ranging from 7.9 to 9.8‰. The original magmas had ?18O values from 7.4 to 9.4‰ (average ?8.0‰) assuming that ?quartz-melt = 0.5‰. A three-stage magmatic evolution is proposed for Azufre. In the first stage, a mantle-derived magma (87Sr/86Sr = 0.70376; ?18O ?5.7‰) ascended to plagioclase-dominated felsic crustal levels (25–50 km depth), assimilating up to 21% of crustal material. This generated a sub-arc parental melt with 87Sr/86Sr ?0.705 and ?18O ?6.5‰. The second stage involves contamination of the parental magma by assimilation of up to 25% of crust with higher 87Sr/86Sr ratios (0.714) and ?18O (6.4–11.8‰) at upper crustal levels (10–25 km depth). This upper crust corresponds to partially molten zones which coincides with the location of the Altiplano-Puna Magma Body. The generated melts have 87Sr/86Sr ratios up to ?0.7075 and ?18Omelt 8.5–9.4‰, which fractionates high-?18O quartz (9.0–9.8‰). The final stage occurred at shallow crustal levels (<10 km depth) where the magmas underwent fractional crystallization during assimilation of crustal material, which due to high-temperature hydrothermal alteration had low ?18O value (?18Omelt 7.4–8.5‰). During this stage, high-?18O quartz of the previous stage remains as antecrysts, coexisting with the low-?18O quartz (?18Oquartz 7.9–9.0‰) fractionated at shallow depths. © 2023 Elsevier Ltd